Pneumatic classifier system



Nov. 24, 1959 H. e. LYKKEN ETAL 2,914,172

- PNEUMATIC CLASSIFIE-IR SYSTEM Ffled May 2, 1955 Sheets-Sheet 1 FIEIZ E i INVENTORS flu/Ry 6 lyxmr-w BY W/LL/AMMLYKKE/v Nov. 24, 1959 H. s. LYKKEN ETAL 2,914,172

PNEUMATIC CLASSIFIER SYSTEM V Filed May 2, 1955 2 Sheets-Sheet 2' INVENDTOIU Ila/Ry 6-1 (ya mg BY WuAM/tLY/ms/v States Patent PNEUMATIC CLASSIFIE'R SYSTEM Henry G. Lykken, Minneapolis, and William H. Lykken, Edina, Minn.. assignors to The Microcyclomat Co., Minneapolis, Minn., a corporation of Delaware Application May 2, 1955, Serial No. 505,118

Claims. (Cl. 209-144) This invention relates to a machine for classifying dry pulverulent material by segregating any desired particle size and finer from the coarser fraction with precision regulation of particle size extracted. 7

The apparatus of this invention is particularly adapted to operate in conjunction with a mill for reducing dry pulverulent material to a high state of fineness substantially free from oversize. Although not so limited, the classifier of this invention is especially adapted to operate with grinders of the type described "in the copending United States applications of Henry G. Lykken and William H. Lykke'n, Serial Nos. 468,764, filed November 15, 1954, and 497,194, filed March 28, 1955.

In fine grinding, it is essential to continuously remove the desired particle size material and finer from the mill load with a substantial air flow through the mill. This air flow will carry with it a percentage of oversize that must be segregated andreturned to the grinding zone.

The principal object of this invention is to provide a classifier for segregating dry pulverulent material of any desired particle size and finer from the coarser fraction in a mill air flow with precision regulation of the particle size extracted and return of the oversize for further reduction.

Other objects of the invention will become apparent as the description proceeds. 7

To the accomplishment of the foregoing and related ends, this invention then comprises the features herein after fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.

The invention is illustrated by the drawings, wherein the same numerals "refer to corresponding parts and in which:

Figure l is a vertical elevation partly in section of the classifier 'of this invention taken along the line :11 and in the direction of the arrows of Figure 2; and

Figure 2 is a cross-section taken on the line 22 and in the direction of the arrows of Figure l.

2,914,172 Patented Nov. 24, 1959 which serves as a feed inlet-oversize return duct. The housing 10 is enclosed by two end plates 16 and 17. The rotor housing is preferably split, as shown, to facilitate change of classifiers, repairs, etc.

The duct formed by wall portions 14 and 15 and the lower portions of end plates 16 and 17 is connected with the discharge of a grinder or pulverizer, and may be shaped to accommodate itself to the particular mill with which it is used. As here illustrated, the classifier is mounted directly on top of a pulverizer of the type described in application Serial No. 497,194, indicated gen- Broadly stated, the invention comprises apparatus adapted to receive the gas flow containing ground particles from a mill or grinder substantially along the length of a centripetal classifier rotor, whirling the fluidal stream of particles around the rotor, setting up a vortex action and withdrawing the particles -of desired size through the classifier rotor by a fan-induced gas fiow, while throwing out the oversize particles and returning them to the mill for regrinding.

Referring now to the drawings, the classifier comprises a generally cylindrical involute housing 10 enclosing a classifier rotor 11. The involute classifier housing wall 12 encloses about three-fourths of the rotor surface with one lower quadrant being left open. A generally tangential depending wall section 14 and a generally radial depending wall section '15 outline a rectangular chamber erally at 18. The classifier need not, however, be mounted on a mill, but may merely be connected to a mill by suitable ducts.

End plate 17 is provided with an enlarged central aperture through which one end of the classifier rotor passes. A fan housing 19 enclosed by a further end plate 2%! is mounted on the classifier housing adjacent this aperture in end plate 17.

A suitable bearing structure is mounted at each end of the unit outside of end plates 16 and 20. The details of construction of the bearings are within the province of mechanical design and need not be further explained here, except to state that the bearings are preferably of the roll or ball bearing type, and they are adequately sized to carry the'rotor of the classifier and fan at the speeds desired and are adequately protected against the entrance of abrasive material into the bearings.

Upon the bearings there is mounted a horizontal shaft 21 extending through each of the end plates 'ruriningth'e entire lengthof the classifier and fan housings and forming the axis thereof. The'shaft may be rotated by means of a pulley (not shown) mounted 'on the projecting end of the shaft and belted to any'suitable motor. Alternatively, the shaft may be driven directly by a motor of suitable design.

The shaft 21 is enlarged and reinforced by a plurality of truncated conical keyedspacing members 22 which define the core of an annular axial duct or passage of gradually increasing cross-section through the classifying rotor. Spacing members 22 are positioned by cylindrical sleeves 24 and 25 keyed to shaft 21.

A rotor end disc 26 is mounted at one end of .the shaft within the classifier housing. A similar end disc 27 having a larger annular opening is mounted on the shaft at the other end of the classifier housing. Disc 27 is supported by annular ring 28 which extends through the annular opening in end plate 17 and is held in position by splines 29. Mounted on bolts between end discs 26 and 27 are a plurality of classifier discs 30 of somewhat lesser diameter held spaced apart by means of washers 31 or similar spacer means. The inner edges of discs 31] define the outer surfaces of the annular axial discharge duct for the wanted fine particles.

The classifier rotor may be of the construction, as illustrated, or alternatively may be in any of the forms described in copending United States applications, Serial Nos. 410,854; 306,126, now Patent No. 2,741,366, issued April 10, 1956; 278,239, now Patent No. 2,754,967, issued July 17, 1956; or similar centripetal classifying rotors.

Radial fan blades 32 are supported between a fan disc 34 mounted on sleeve 25 of shaft 21 and a ring disc 35 mounted on annular ring 28. The fan housing is provided with a discharge outlet 36 for removing the desired fine particles. In the preferred form of the invention, the air flow through the mill and classifier is provided by an independently driven exhaust fan (not shown) discharging directly to a collector system for the finished product, although fan 32 may, in some instances, serve this function. The primary purpose of this fan is to insure uniform inlet velocity at the periphery of the classifier rotor. The exhaust fan, where used, is connected in series with the classifier fan.

The air and airborne material inlet and tailings outlet defined between the end plates 16 and 17 and housing wall portions 14 and 15 is divided longitudinally by a generally vertical partition or bafiie 37 extending the length of the housing from adjacent to the rotor to the bottom of the inlet duct. The larger area so defined between vertical tangential wall portion 14 and battle 37 serves as an air and material inlet. The smaller area defined between generally vertical and radially depending wall portion 15 and baffle 37 serves as a tailings return and air trap for liberating and recirculating air bearing the heavier particles.

An adjustable skimmer 38 is positioned adjacent the bottom of the rotor housing to draw oh. the coarser particles which are thrown outwardly against the housing wall. The skimmer extends the length of the housing and comprises a generally vertical portion spaced apart from wall portion 15, and a generally horizontal portion 39 overlying and slightly spaced apart from the edge of involute housing wall 12 at its juncture with wall portion 15. The skimmer is adjustably supported in brackets 40 at either end of the classifier for vertical movement to vary the width of the throat formed with the rotor housing wall.

The principle of classification in this invention involves drawing air laden with pulverulent material from a grinding mill, such as, for example, that indicated at 18, through the duct defined by end plates 16 and 17, housing wall portion 14 and baffie 37 radially inward into the classifier rotor at a controlled and regulated velocity and drag, against a controlled and regulated centrifugal force outward. The velocities and forces are regulated and controlled. depending upon the materials being treated, by varying the speed of rotation of the rotor and the air velocities.

The particle size is controlled by varying the rotative velocity of the rotor and the velocity of the air through the rotor. Although there is a best centrifugal force for any given material and particle size, in practice the rotor is set for the best practical operating speed, and the wanted particle size is obtained by regulating the air fiow through the rotor.

The material laden air is drawn up into the classifying chamber and is circulated continuously around the classifier rotor as it is drawn into the rotor. The coarser material, due to centrifugal action, circulates on the rotor housing wall. Only the desired particle size and finer enters the rotor between classifier discs 30 and is drawn off through the axial passage and discharged to a collector system.

The adjustable skimmer 38 continuously peels off and removes the layer of coarser material circulating on the wall and returns it to the grinding zone of the mill for further reduction. The air in the skimmed-E material is liberated in the air trap in conjunction with the skimmer and is recirculated in the rotor housing. The skimmed-off particles are returned with little or no air to the mill.

A relatively small percentage of fines will be returned to the mill with the oversize, and some relatively small amount of oversize will continuously recirculate. However, the principle of operation only calls for limiting the percentage of oversize in the circulating load.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible in view of the prior art.

What we claim is:

1. A pneumatic classifier for dry pulverulent material comprising a classifier housing and fan housing adjacent thereto, a rotor journalled for rotation horizontally within the housings, centripetal classifying means mounted on the rotor within the classifier housing and fan means mounted on the rotor within the fan housing, an axial duct leading from the classifying means to the fan, tangential discharge means from said fan housing, a chamber mounted in the classifier housing along and under one lower quadrant thereof, said chamber being divided by a longitudinal wall to form a material and air inlet and a separate tailings outlet within said chamber, said outlet being in communication with said inlet above and below said dividing wall, and means within said tailings outlet extending the length of the rotor adjacent to the bottom of the classifier housing wall for skimming off oversize particles.

2. A classifier according to claim 1 further characterized, in that the inlet-outlet chamber is open at the bottom and adapted to be mounted over the material discharge opening on top of a mill.

3. A classifier according to claim 1 further characterized, in that said classifier housing is in the form of a generally cylindrical involute.

4. A classifier according to claim 1 further characterized, in that said classifying means comprises a plurality of spaced apart annular discs, the spaces between said discs communicating with said axial duct.

5. A pneumatic classifier for dry pulverulent material comprising a generally cylindrical classifier housing and a fan housing adjacent thereto, a rotor journalled for rotation horizontally within said classifier and fan housings, centripetal classifying means mounted on said rotor within the classifier housing, radial fan means on said rotor within the fan housing, an axial duct leading from said classifying means to said fan, tangential discharge means from said fan housing, a generally rectangular chamber mounted in the classifier housing along and under one lower quadrant thereof extending the length of the rotor, said chamber being divided by a longitudinal wall to form a generally tangential material and air inlet and a separate tailings outlet within said chamber, said outlet being in communication with said inlet above and below said dividing wall, and means within said tailings outlet extending the length of the rotor adjacent to the bottom of the classifier housing wall for skimming ofif oversize particles from the housing wall.

6. A classifier according to claim 5 further characterized, in that the generally rectangular inlet-outlet chamber is open at the bottom and adapted to be mounted over the material discharge opening on top of a grinding mill.

7. A classifier according to claim 5 further characterized, in that said generally cylindrical classifier housing wall is in the form of an involute.

8. A classifier according to claim 5 further characterized, in that said classifying means comprises a plurality of spaced apart annular discs, the spaces between said discs communicating with said axial duct.

9. A pneumatic classifier for dry pulverulent material adapted for use in conjunction with a grinding mill, said classifier comprising a generally cylindrical involute classifier housing and a fan housing adjacent thereto, a rotor journalled for rotation horizontally within said classifier and fan housings, centripetal classifying means mounted on the end of said rotor within the classifier housing, radial fan means on the other end of said rotor within the fan housing, an annular axial duct leading from said classifying means to said fan, tangential discharge means fromsaid fan housing, a generally rectangular chamber mounted in the classifier housing along and under one lower quadrant thereof, said chamber being divided longitudinally by a vertical wall extending the entire length of the classifier housing to form a generally tangential material and air inlet from said mill and a separate tailings outlet for returning oversize particles to said mill within said chamber, said outlet being in communication References Cited in the file of this patent between said discs communicating with said axial duct. 10 2,592,231

UNITED STATES PATENTS.

Stebbins Nov. 6, 1900 Schutz June 3, 1919 Lykken Dec. 30, 1930 Tenney July 25, 1933 Chesler Mar. 30, 1943 De Fligue Oct. 31, 1949 Allstatt Apr. 8, 1952 

